Waterproof ammonium nitrate explosive



United States Patent Pennsylvania No Drawing. Filed Aug. 31, 1959, Ser.No. 836,882 6 Claims. (Cl. 149-7) This invention relates to a waterproofammonium nitrate explosive composition and, more particularly, itrelates to a waterproof ammonium nitrate explosive composition whereinthe particles of ammonium nitrate are coated with apolyethylene-microcrystalline wax coating composition.

Ammonium nitrate has been used for many years as an ingredient inexplosive compositions. However, it is only during the last severalyears that ammonium nitrate has been used as an explosive withoutspecial compounding and packaging. In particular, it has been found thatammonium nitrate produced for fertilizers may be employed as aninexpensive source of the chemical since explosive technology hasadvanced to a point such that advantage may be taken of the availabilityand low cost of such materials.

When ammonium nitrate was employed heretofore as the primary ingredientof an explosive composition it was mixed with carbon black, sawdust,sulfur or other combustible materials to utilize the excess oxygenavailable in the ammonium nitrate decomposition reaction. Even morerecently fuel oil has been admixed with ammonium nitrate to produce anexplosive in which the fuel oil apparently enters into the primarydecomposition reaction since the speed of the decomposition of theammonium nitrate is materially increased. All of these ammonium nitrateexplosive compositions, however, have been limited as to their use sinceammonium nitrate is exceedingly soluble in water. Accordingly, it wasnecessary to use the ammonium nitrate in a form in which its moisturecontent was rather low and in drill holes which were dry. Since theprincipal uses of this low cost type explosive were in construction,mining and quarrying operations, often times it was impossible to employammonium nitrate explosives since the drill holes were not dry or werein locations where they could not be kept dry. Accordingly, the needarose for a waterproof ammonium nitrate explosive composition.

It was also found necessary that the waterproofed ammonium nitratecomposition have a density greater than that of water so that theammonium nitrate composition would stay in contact with the dynamitedetonator at the bottom of the drill hole in the event that the drillhole became filled with water. In other words, it was necessary that theammonium nitrate composition not float or be capable of being washed outof a drill hole because of its density being less than that of water.Moreover, it was found that the degree of-water resistance of theammonium nitrate composition should be sufficiently great so that if theammonium nitrate explosive composition remained in contact with water ina drill or bore hole for an extended period of time, it would notdissolve sufliciently to raise the density of the water and therebycause the ammonium nitrate explosive particles to float out of the borehole or float out of contact with the detonation primer at the bottom ofthe hole.

A waterproof ammonium nitrate composition having improved detonationcharacteristics and a density greater than that of water now has beenproduced in which the ammonium nitrate particles are coated withamicrocrystalline wax composition to render the particles waterproof andsimultaneously provide a combustible material for the utilization of theexcess oxygen resulting from the ammonium nitrate decompositionreaction.

It is an object, therefore, of this invention to provide a waterproofammonium nitrate explosive composition.

It is another object of this invention to provide a waterproof ammoniumnitrate explosive composition having a density greater than that ofwater.

It is another object of this invention to provide a waterproof ammoniumnitrate explosive composition wherein the ammonium nitrate particles arecoated with a mi-- crocrystalline wax composition.

It is another object of this invention to provide a waterproof ammoniumnitrate composition in which the ammonium nitrate particles are coatedwtih a combustible composition which will utilize the excess oxygenavailable from the ammonium nitrate decomposition reaction.

Additional objects will be apparent from the following description ofthe invention and the claims.

In accordance with this invention ammonium nitrate particles are coatedwith a minor amount of a microcrystalline wax composition whichcomposition contains minor quantities of polyethylene.

The ammonium nitrate may be in the form of prills, granules, orcompacted granules, all of which forms are available commercially. It ispreferred that the ammonium nitrate be in a relatively pure formcontaining at most only minor amounts of impurities or inertingredients. Ammonium nitrate fertilizer grades frequently contain minorportions, approximately 0.5 percent by weight, of a rosin to prevent theammonium nitrate particles from agglomerating and render themfree-flowing. Other fertilizer grade ammonium nitrate compositionscontain small amounts up to 3 percent by weight of diatomaceous earth orclays which are incorporated for the purpose of preventing the particlesfrom agglomerating.

While these fertilizer grade materials may be employed in the explosivecompositions of this invention, ammonium nitrate grades not containingthese additives or containing only very small amounts of these additivesare preferred since the wax coating applied to the particles inaccordance with this invention will serve as a non-agglomerating agentin addition to its functions as a waterproofing agent and sensitizingagent. Ammonium nitrate compositions containing rosin or clay are notpreferred for the additional reason that they have been found to havedetonation velocities lower than those of ammonium nitrate compositionsin which these additives are absent. The ammonium nitrate coated withthe polyethylene-microcrystalline wax composition in accordance withthis invention has surprisingly much improved detonationcharacteristics, the detonation velocities obtainable being higher thanthose of the uncoated material.

The microcrystalline waxes, sometimes designated as amorphous orpetrolatum waxes, which are utilized as the major component of thecoating compositions of this invention may range in melting point fromF. to 190 F. as measured by ASTM Method D-l27. These waxes which areobtained by the solvent extraction and deoiling of heavy petroleumdistillate or residuum stocks are further characterized by beingrelatively light in color ranging from 1 /2 to 2 as measured by ASTMMethod D- and having a viscosity of from 70 to about 90 Saybolt secondsUniversal at 210 R, an oil content not in excess of from 1.0 to 1.5percent as measured by ASTM Method D-721, and a penetration at 77 F. offrom 9 to 30 as measured by ASTM Method D-l321.

The polyethylene polymers which are incorporated in the microcrystallinewax to produce the finished wax coating composition preferably have anaverage molecular weight ranging from 2,000 to 25,000. Such polyethylenepolymers are available commercially from a number of differentmanufacturing companies. In general, polymers having a molecular weighttoward the lower end of the range specified are preferred. The

compositions are prepared by melting the microcrystalline wax andgradually introducing the polyethylene into the wax by vigorousagitation.

In order to coat the ammonium nitrate particles, they are heated to atemperature of 25 F., preferably, and the melted microcrystallinewax-polyethylene composition is poured thereover and mixed therewith fora period of about one-half hour in order to insure thorough coating ofeach ammonium nitrate particle with the wax composition. The coatedparticles are then spread out in a thin layer and allowed to cool anddry with occasional gentle agitation to prevent agglomeration during thedrying step.

It has been found that the amounts of polyethylenemicrocrystalline waxcomposition used to coat the ammonium nitrate are extremely critical andshould range from 5.0 to 7.0 percent by weight based on the total Weightof the coated ammonium nitrate. Quantities of wax composition less than5 percent by weight give insufiicient waterproofing whereas quantitiesin excess of 7 percent by weight decrease the density of the particlesof the finished coated product to such an extent that they will tend notto sink in water. Moreover quantities of wax composition in excess ofabout 7 percent by weight decrease the detonation velocities of thefinished explosive. Preferably the quantity of wax composition used tocoat the ammonium nitrate particles should range from 5.5 to 6.5 weightpercent based on the weight of the finished coated ammonium nitrate.About 6.0 percent by weight of the wax composition based on the weightof the finished product has been found to produce the best results fromthe standpoint of density, waterproofness, and detonation velocitycharacteristics of the finished product.

The amount of polyethylene incorporated in the microcrystalline waxshould range from 1.0 percent by weight to 5.0 percent by weight basedon the total weight of the polyethylene-microcrystalline wax compositionin order to produce a coating composition which will provide the desiredwaterproofing characteristics to the ammonium nitrate. Preferably theamount of polyethylene should be about 3.0 percent by weight based onthe weight of the polyethylene-microcrystalline wax composition sincecompositions containing this amount of polyethylene have been found togive the greatest degree of waterproofing to the ammonium nitrate.

The following examples are provided for the purpose of illustratingcertain specific embodiments of the invention and in addition for thepurpose of showing the criticality of certain features of the invention.

The ammonium nitrate employed in the following examples was a commercialprilled fertilizer grade containing between 1.0 and 2.0 percentinorganic clay material as an anti-agglomerating agent.

The microcrystalline wax employed in the examples had a melting point or175 F., a color ranging between 1% and 1% as measured by the ASTM MethodD-155, a viscosity of 80 Saybolt seconds Universal at 210 F and an oilcontent of 1.0 percent.

The polyethylene polymer employed in the examples was a commercial gradehaving an average molecular weight of 2,000.

A number of wax compositions were prepared in which the quantity ofpolyethylene added to the microcrystalline wax was varied. Variousamounts of these compositions were employed to coat the ammoniumnitrate. In order to determine the waterproofing qualities of thesecompositions, a weighed quantity of the coated ammonium nitrate wasimmersed in water for one hour at approximately 73 F., after which timethe coated particles were dried and reweighed to determine the loss inweight.

The loss in weight represents ammonium nitrate which has dissolved inthe water and thereby been lost from the total quantity Accordingly alow value for weight loss corresponds to high waterproofingcharacteristics for the wax coating.

The polyethylene microcrystalline wax compositions Were compared withthe microcrystalline wax alone and with compositions containing arefined petroleum paraffin wax instead of the microcrystalline wax, suchparaffin wax having a melting point of F. to 132 F. The compositions andtheir waterproofing characteristics are set forth in the table.

Table Composition Weight percent wax Weight Example No. comp. basedpercent Mlero- Polyon wt. of loss crystalline ethylene Coated WaxProduct 1 Refined paraffin wax, 130 F.132 F. melting point.

It will be seen by comparing the weight loss obtained in Examples 1, 2,and 3 with that of Example 4 that the quantity of polyethylene in themicrocrystalline wax should range between 1.0 and 5.0 percent by weightbased on the weight of the polyethylene-microcrystalline wax compositionand that a composition containing 3.0 percent by weight of polyethyleneshows superior waterproofing characteristics.

It Examples 1, 2, and 3 are compared with Example 6 it will be seen thatthe quantity of wax composition which should be applied for coating theammonium nitrate is extremely critical. Comparison of Example 2 withExamples 5 and 7 shows that a refined parafiin wax cannot be substitutedfor the microcrystalline wax to produce a waterproofing coatingcomposition in accordance with the objects of this invention.

The waterproofed ammonium nitrate particles of these examples had adensity greater than that of water.

The waterproofed product of Example 2 was detonated in order to measureits detonation characteristics. It was found that the ammonium nitratecoated with the composition of Example 2 had a detonation velocity of2,266 meters per second as compared with non-waterproofed andnon-sensitized ammonium nitrate which generally has a detonationvelocity of from 1,500 to 2,000 meters per second, thus demonstratingthat a satisfactory waterproofed ammonium nitrate explosive compositionmay 'be prepared in accordance with this invention.

I claim: 4

1. A waterproof ammonium nitrate explosive composition consistingessentially of ammonium nitrate particles coated with from 5.0 percentby weight to 7.0 percent by weight based on the total weight of thecomposition of a polyethylene-petroleum hydrocarbon microcrystalline waxcoating composition wherein the polyethylene ranges from 1 percent byweight to 5 percent by weight based on the total weight of thepolyethylene-petroleum hydrocarbon microcrystalline wax coatingcomposition.

2. A waterproof ammonium nitrate explosive composition consistingessentially of ammonium nitrate particles coated with from 5.5 percentby weight to 6.5 percent by weight based on the total weight of thecomposition of a polyethylene-petroleum hydrocarbon microcrystalline waxcoating composition wherein the polyethylene ranges from 1 percent byweight to 5 percent by weight based on the total weight of thepolyethylene-petroleum hydrocarbon microcrystalline wax coatingcomposition.

3. A waterproof ammonium nitrate explosive composition consistingessentially of ammonium nitrate particles coated with about 6.0 percentby weight based on the total weight of the composition of apolyethylene-petroleum hydrocarbon microcrystalline wax coatingcomposition wherein the polyethylene ranges from 1 percent by weight to5 percent by weight based on the total weight of thepolyethylene-petroleum hydrocarbon microcrystalline wax coatingcomposition.

4. A waterproof ammonium nitrate explosive composition consistingessentially of ammonium nitrate particles coated with from 5.0 percentby weight to 7.0 percent by weight based on the total weight of thecomposition of a polyethylene-petroleum hydrocarbon microcrystalline waxcoating composition wherein the polyethylene constitutes about 3 percentby weight of the polyethylenepetroleum hydrocarbon microcrystalline waxcoating composition.

5. A waterproof ammonium nitrate explosive composition consistingessentially of ammonium nitrate particles coated with from 5.5 percentby weight to 6.5 percent by weight based on the total weight of thecomposition of a polyethylene-petroleum hydrocarbon microcrystalline waxcoating composition wherein the polyethylene constitutes about 3 percentby weight of the polyethylene- 10 bon microcrystalline wax coatingcomposition.

References Cited in the file of this patent UNITED STATES PATENTS2,274,822 Cairns et al Mar. 3, 1942 2,513,391 Zenftman July 4, 1950FOREIGN PATENTS 649,613 Great Britain Jan. 31, 1951 OTHER REFERENCESKirk and Othmer: Encyclopedia of Chemical Technology, volume 10, page953.

1 UNITED STATES PATENT OFFICE Patent N0 3,013,872

December l9, 1961 Bryant Ca Winchell l It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

0 Column 3, line 5, for "25 Ft" read 225 F, =-e

Signed and sealed this 24th day of April 19 62a (SEAL) zittestz ESTON, eJOHNSON Attesting Officer DAVID L, LADD Commissioner of Patents UNITEDSTATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 3 O13 872December 19 1961 Bryant C, Winchell It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 3 line 5 for "25 F0" read M 225 Eo Signed and sealed this 24thday of April 1962,

(SEAL) V Attestz- My, ESTONH er JOHNSON DAVID LIIL Attesting Officer"Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OFCORRECTION Patent No, 3 013372 December 19 1961 Bryant C, Winchell It ishereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 5 for "25 FD" read W 225 F. a

Signed and sealed this 24th day of April 1962 (SEAL) Attest:

ESTON Gm, JOHNSON DAVID J Commissioner of Patents Attesting Officer

1. A WATERPROOF AMMONIUM NITRATE EXPLOSIVE COMPOSITION CONSISTINGESSENTIALLY OF AMMONIUM NITRATE PARTICLES COATED WITH FROM 5.0 PERCENTBY WEIGHT TO 7.0 PERCENT BY WEIGHT BASED ON THE TOTAL WEIGHT OF THECOMPOSITION OF A POLYETHYLENE-PETROLEUM HYDROCARBON MICROCRYSTALLINE WAXCOATING COMPOSITION WHEREIN THE POLYETHYLENE RANGES FROM 1 PERCENT BYWEIGHT TO 5 PERCENT BY WEIGHT BASED ON THE TOTAL WEIGHT OF THEPOLYETHYLENE-PETROLEUM HYDROCARBON MICROCRYSTALLINE WAX COATINGCOMPOSITION.